I don't think people particularly care whether something is legal or not when it comes to drugs. It's not like when heroin becomes legal everyone will start to take it. And even if somehow a kid obtains heroin from a legal source they'll know dosage strength and doctors will know what to do. If you buy from a dealer you can't know what exactly it is. Many deaths were caused by accidental overdose when dealer added cheap Chinese fentanyl to make it "stronger" but was too lazy to mix it properly. When you buy legal alcohol you can be sure you won't get methanol poisoning or ingest hand sanitizer.